The invention relates to a method for avoiding a runaway condition of an internal combustion engine, a computer program, a computer readable medium, a control unit, an engine system and a vehicle.
The invention can be applied in heavy-duty vehicles, such as trucks, buses and construction equipment. Although the invention will be described with respect to a heavy-duty vehicle, the invention is not restricted to this particular vehicle, but may also be used in other vehicles such as working machines and cars.
In an internal combustion engine, such as heavy duty vehicle diesel engine, there might be a risk of the engine entering a so called runaway condition, which, although rare, may seriously damage the engine. In such a condition the engine draws extra fuel from an unintended source, overspeeds, and may be destroyed by mechanical failure or seizure. The extra fuel, forming an undesired or unrequested introduction of hydrocarbon into the cylinders of the engine, may enter via the engine air intake system. The unrequested hydrocarbon may include, for example, hydrocarbon of fuel and engine oil. For example, a mixture of excess fuel and oil may be vented from the engine crankcase into the air intake via a crankcase ventilation system of the engine. The excess fuel and oil may enter the crankcase due to leakage from a fuel system (e.g. from pumps, injectors and connecting pipes), an oil leak in the seal of a turbocharger, or leakage from the cylinders into the crankcase. Further possible causes to engine runaway conditions include undesired oil or fuel leakage into the cylinders, which does not combust completely and gets re-introduced via an exhaust gas recirculation (EGR) path, and oil introduced at an air intake compressor through damaged seals in the compressor shaft.
In diesel engines using diesel oil fuel, leakage of fuel into the crankcase may be managed by a crankcase ventilation system based on the evaporation of the fuel from the warm oil in the crankcase. In a closed crankcase ventilation system so called blow-by gas from the crankcase is returned to engine air intake for combustion. However, when the fuel is volatile such as dimethyl ether (DME), a high leakage rate to the crankcase may provide correspondingly high evaporation rate, thus posing an engine runaway risk by a closed crankcase ventilation system. Providing instead an open crankcase ventilation system provides as a result ventilating the vaporized fuel to the atmosphere, which may result in a safety hazard, increases the environmental burden and may not be allowed in some jurisdictions.
U.S. Pat. No. 9,074,543 discloses, in response to a detection of a cylinder imbalance indicating oxidation of accumulated hydrocarbons, limiting the engine speed and load to reduce further hydrocarbon accumulation.
A problem with known unrequested hydrocarbon cylinder introduction detections strategies in vehicle engine systems is a lack of reliability resulting in false indications and executions of runaway risk reducing measures, such as a limp-home mode and/or blow-by gas emissions to the atmosphere, which may be un-convenient to a user of the vehicle and environmentally burdensome. The lack of reliability may be caused by highly transient operating patterns of vehicle engines. Thereby it may be impossible to accurately avoid needless triggering of runaway safety measures.
An object of the invention is to provide an internal combustion engine runaway risk detection strategy with an improved accuracy and reliability. A further object of the invention is to avoid an overreaction to an indication that an internal combustion engine is at a risk of entering a runaway condition, particularly where the engine uses a volatile fuel such as dimethyl ether (DME). Another object is to provide in a cost effective manner a balanced reaction to an indication that an internal combustion engine is at a risk of entering a runaway condition.
An aspect of the invention provides a method for avoiding a runaway condition of an internal combustion engine comprising a cylinder, comprising detecting an operational characteristic of the engine, presumed to be caused by an unrequested introduction of hydrocarbon into the cylinder, characterized by derating the engine in dependence of the detection, and performing while the engine is derated a test procedure to detect an unrequested introduction of hydrocarbon into the cylinder.
It is understood that derating the engine in dependence of the detection may involve derating the engine in response to the detection.
The derating provides a quick response to reduce a risk of the engine entering a runaway condition in case the detected operational characteristic of the engine is caused by unrequested introduction of hydrocarbon into the cylinders. However, the detected operational characteristic may have causes other than such unrequested hydrocarbon cylinder introduction. Since the cause of the detection cannot be established with a high degree of certainty, the derating is executed instead of an engine shutdown which may in itself cause a safety risk, e.g. where the vehicle is moving on a busy road. By performing the test procedure while the engine is derated, it may be established with a relatively high degree of certainty, after the detection of the operational characteristic of the engine, whether or not there is an unrequested introduction of hydrocarbon into the cylinders.
Thus, the test procedure may provide an additional, more certain level in the diagnosis of the engine system according to embodiments of the invention. This means that the detection of the operational characteristic of the engine provides a first preliminary indication that there is an unrequested introduction of hydrocarbon into the cylinder. Since this detection may have a relatively low level of certainty as to whether it is caused by such a hydrocarbon introduction, the derating provides an engine runaway risk reducing effect, while a more certain diagnosis may be provided by the test procedure. Thereby, an overreaction to the uncertain preliminary indication, e.g. by an engine shutdown, may be avoided.
The method according to embodiments of the invention may be executed with hardware provided in known modern internal combustion engine systems. Therefore the invention may provide a cost effective way of providing a balanced reaction to an indication that an internal combustion engine is at a risk of entering a runaway condition. The method may advantageously be carried out in an on-board diagnostics (OBD) system of a vehicle.
Therefore, the invention may provide a cost efficient way of improving the accuracy and reliability of a vehicle OBD and safety system, to prevent engine runaway conditions and minimise the risk of false alarms. In particular, the method according to embodiments of the invention may the used to increase the accuracy and reliability of engine runaway risk detection in cases where the risk of such a condition is increased due to the use of a volatile fuel, such as dimethyl ether (DME).
The test procedure may be initiated in dependence on said detection of the operational characteristic of the engine and/or the derating of the engine. Derating the engine may comprise reducing a maximum torque of the engine. Thereby an effective way of reducing the risk of an engine runaway condition while the test procedure is carried out is provided.
Preferably detecting an operational characteristic of the engine comprises determining during operation of the engine a first value of an engine system parameter, and comparing the first value to a first predetermined threshold value of that parameter. The engine system parameter may be a difference between the temperature of exhaust gases produced by the engine and an expected temperature of exhaust gases produced by the engine. However, in some embodiments, the engine system parameter may be the temperature of exhaust gases produced by the engine. Thereby an easy and quick way of providing the first indication of the engine runaway condition is provided.
Preferably, derating the engine in dependence of the detection comprises derating the engine in dependence of the comparison of the first engine system parameter value to the first predetermined threshold value. Preferably, derating the engine in dependence of the detection comprises derating the engine if the first engine system parameter value exceeds the first predetermined threshold value. Derating the engine may comprise reducing a maximum torque of the engine, e.g. to 85% of the maximum torque when the engine is not derated.
Preferably, where the engine is provided in a vehicle, the method comprises issuing in dependence on the detection of the operational characteristic of the engine an instruction to a driver of the vehicle to allow the engine to idle. It is understood that issuing the instruction in dependence on the detection of the operational characteristic may involve issuing the instruction in response to the detection of the operational characteristic. The method may also comprise determining in dependence on the detection of the operational characteristic of the engine whether or not the engine is idling. Thereby, it may be determined to not initiate or perform the test procedure if the engine is not idling.
Thus, it may be advantageously ensured before performing the test procedure that a condition that may be required for the procedure, i.e. engine idling, is present. Idling may in a vehicle involve an engine system operation where no gear is engaged, i.e. where the engine is uncoupled from a drivetrain and a driver engine control device, such as a gas pedal, is not manipulated, e.g. depressed, to change fuelling. The vehicle may comprise one or more sensors detecting whether or not an external engine load, other than a load provided by the drivetrain, is present, for instance sensors detecting engagement of various ancillary equipment, such as an engine fan, an air compressor, systems actuated via power take-off, etc. In some embodiments, such other loads may be detected. In case such a detection is made, it may be determined to not proceed with the test procedure until the load is removed, and/or a request may be issued to an engine operator or a vehicle driver to disengage the load, before executing the test procedure.
In some embodiments, the derating may itself alert the driver and induce him or her to allow the test procedure by idling the engine. The driver feeling a loss of power may tend to let the engine idle as an “instinctive” way of troubleshooting. Where an instruction is issued to the driver, e.g. by a message on a dashboard of the vehicle, this would likely lead to the engine being left alone to idle providing a chance to quickly exercise the test procedure.
In advantageous embodiments, where the engine comprises an inlet guide for guiding air to the cylinder, and the cylinder comprises a piston connected to a crankshaft, the engine further comprising a crankcase for housing the crankshaft, and a crankcase ventilation system which is arranged to assume an open condition in which a fluid in the crankcase is guided to the atmosphere, and a closed condition in which a fluid in the crankcase is guided to the inlet guide, the test procedure comprises
determining a first value of an operating parameter while the engine is operated in a first predetermined operating condition with the crankcase ventilation system in the closed condition,
determining a second value of the operating parameter while the engine is operated in the first predetermined operating condition with the crankcase ventilation system in the open condition, and
determining, based at least partly on the first and second operating parameter values, whether or not there is an unrequested introduction of hydrocarbon into the cylinder.
Thus, the test procedure may involve operating the engine with the crankcase ventilation system in one of the closed and open conditions, and subsequently operating the engine in the other of the closed and open conditions. The first and second operating parameter values determined in a respective of the closed and open conditions are compared. The method may comprise determining, if the difference between the first and second operating parameter values is larger than a predetermined value difference, that there is an unrequested introduction of hydrocarbon into the cylinder. Thereby a particularly effective method of establishing whether there is an unrequested introduction of hydrocarbon into the cylinder, presumably through the crankcase ventilation system, is provided
The first predetermined operating condition may be engine idling. The operating parameter may be the engine rotational speed. Thereby a relevant parameter is used which is detectable by means of available engine monitoring devices. Alternatively, the operating parameter may be some other suitable parameter, such as the exhaust temperature or the crankcase pressure.
Preferably, if the difference between the first and second operating parameter values is larger than a predetermined value difference, the crankcase ventilation system is controlled so as to assume the open condition. Thereby, the risk of an engine runaway condition due to unrequested hydrocarbon introduction into the cylinder via the crankcase ventilation system will be eliminated.
In some embodiments, if the difference between the first and second operating parameter values is larger than a predetermined value difference, the engine may be stopped. Where the engine is provided in a vehicle, stopping the engine may be done by instructing a driver of the vehicle to stop the engine. In some embodiments, if the difference between the first and second operating parameter values is larger than the predetermined value difference, it is determined whether the engine is idling and the engine is stopped if it is determined that the engine is idling. Such a stopping control may be executed by a control unit. Thereby, the risk of an engine runaway condition will be eliminated.
Preferably the method comprises determining while the engine is derated a second value of the engine system parameter, and comparing the second value to a second predetermined threshold value. Thereby, the initiation of the test procedure may be dependent on the comparison of the second engine system parameter value to the second predetermined threshold value. The method may comprise determining to initiate the test procedure if the second engine system parameter value is lower than the second predetermined threshold value. On the other hand, if the second engine system parameter value exceeds the second predetermined threshold value, the engine may be derated further. Derating the engine further may comprise operating the engine in a limp-home mode. Derating the engine further in this manner provides a quick response to reduce a risk of the engine entering a runaway condition. The second engine system parameter value being determined while the engine is derated provides an additional basis for determining an appropriate action in view of a potential engine runaway risk.
Where the engine comprises an inlet guide for guiding air to the cylinder, and the cylinder comprises a piston connected to a crankshaft, the engine further comprising a crankcase for housing the crankshaft and a crankcase ventilation system which is arranged to assume an open condition in which a fluid in the crankcase is guided to the atmosphere, and a closed condition in which a fluid in the crankcase is guided to the inlet guide, the method may comprise, if the second engine system parameter value exceeds the second predetermined threshold value, controlling the crankcase ventilation system so as to assume the open condition. This will reduce the risk of any further unrequested hydrocarbon entering the cylinders via the inlet guide.
It should be noted that where the engine is provided in a vehicle, the crankcase ventilation system may be controlled by a control unit. However, alternatively or in addition the vehicle may comprise manually controllable means for switching the crankcase ventilation system from the closed condition to the open condition. Such means may be provided in the form of a control device, such as a switch, arranged to be manipulated by a driver of the vehicle. In some embodiments, the crankcase ventilation system may be arranged so that a control action via such manually controllable means will have priority over a request from a control unit arranged to control the crankcase ventilation system. In such a system, a control action using the manually controllable means may override a command from the control unit, and enforce a shift to the open condition irrespective, of the command from the control unit.
Preferably, if the second engine system parameter value exceeds the second predetermined threshold value, the engine is stopped. Where the engine is provided in a vehicle, stopping the engine may be done by instructing a driver of the vehicle to stop the engine, or by determining whether the engine is idling and stopping the engine if it is determined that the engine is idling. Where the engine comprises an inlet guide for guiding air to the cylinder, stopping the engine may comprise controlling a throttle valve so as to block the inlet guide. Thereby, the risk of an engine runaway condition may be reduced, e.g. if a catastrophic crankcase fuel leakage has occurred and derating the engine will not prevent the runaway condition. However, if the second engine system parameter value does not exceed the second predetermined threshold value, this may provide an indication that the engine is safe to run, and instead of stopping it the test procedure described above may be executed.
The second predetermined threshold value may be the same as the first predetermined threshold value, or it may be different therefrom.
In advantageous embodiments, where the engine comprises a fuel system for injecting fuel into the cylinder, the method comprises determining while the engine is operated in a second predetermined operating condition a value of an engine operation parameter, comparing the determined engine operation parameter value to a stored value of the engine operation parameter associated with the predetermined engine condition, and determining based at least partly on the comparison whether or not there is an indication of an unrequested introduction of hydrocarbon into the cylinder. The stored engine operation parameter value may be stored in a storage accessible to an engine system control unit. The engine operation parameter value may be a demanded fuel amount to be injected, or a rotational speed of the engine. In some embodiments, the demanded fuel amount and the rotational speed may both form the engine operation parameter, and determined values of the demanded fuel amount and the rotational speed may be compared to respective stored values of the demanded fuel amount and the rotational speed. The second predetermined operating condition may be engine idling. By such embodiments, a determination may be made that there is an indication of an unrequested introduction of hydrocarbon into the cylinder if the difference between the determined engine operation parameter value and the stored engine operation parameter value is larger than a predetermined threshold value.
Thereby, an additional process is provided for determining whether or not there is an unrequested introduction of hydrocarbon into the cylinder. This provides means, in addition to the detection of the operational characteristic of the engine and the test procedure, to obtain an indication of an unrequested introduction of hydrocarbon into the cylinder. In some embodiments, the test procedure may be performed in dependence on the comparison of the determined engine operation parameter value to the stored value of the engine operation parameter. Thereby, performing the test procedure may be avoided if said comparison suggests or indicates that there is no unrequested introduction of hydrocarbon into the cylinder. Where the comparison of the determined engine operation parameter value to the stored value of the engine operation parameter indicates or suggests that there is an unrequested introduction of hydrocarbon into the cylinder, the test procedure follows to provide a more certain determination of whether or not there is such an introduction. Thereby, additional certainty may be provided to the unrequested hydrocarbon cylinder introduction detection, whilst avoiding unnecessary messages or false fault alerts to an operator of the engine or a driver of a vehicle in which the engine is provided, such as a request to allow the engine to idle. Also, unnecessary switching of a crankcase ventilation system to an open condition may be avoided. Such means to detect an indication of an unrequested hydrocarbon cylinder introduction may advantageously be performed without adding any dedicated sensors to the engine system. As an example, in electronically controlled engines there may be a control feature in the form of an idle governor that adjusts the fuelling demand to the injectors in real time in order to keep the idle engine rotational speed at a certain level. If there is an unrequested hydrocarbon cylinder introduction the idle governor may potentially reduce fuelling demand to zero while trying to keep the engine speed at the required level, and such a fuelling demand may advantageously serve as an indication of the unrequested hydrocarbon cylinder introduction.
The method may further comprise, if it is determined that there is not an unrequested introduction of hydrocarbon into the cylinder, adjusting the stored engine operation parameter value. E.g. where the above described determination, based at least partly on the comparison of the engine operation parameter value to the stored engine operation parameter value, whether or not there is an indication of an unrequested introduction of hydrocarbon into the cylinder, is followed by the above described test procedure, the method may further comprise, if it is determined by the test procedure that there is not an unrequested introduction of hydrocarbon into the cylinder, adjusting the stored engine operation parameter value.
For example, if the test procedure indicates, in contradiction to the determination based at least partly on the comparison of the engine operation parameter value to the stored engine operation parameter value, that there is no unrequested introduction of hydrocarbon into the cylinder, it may be assumed that the stored engine operation parameter value is incorrect, and therefore it is advantageously adjusted. The adjustment may involve replacing in a storage accessible to an engine system control unit the stored engine operation parameter value with the determined engine operation parameter value. The discrepancy between the determined engine operation parameter value and the stored engine operation parameter may be caused e.g. by a “drift” in the parameter values due to the operation history of the engine. The adjustment of the stored engine operation parameter value will further reduce the risk of the overreactions due to false indications of engine runaway conditions. Thereby, a learning algorithm with a parameter drift compensating feature is provided.
Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.